From ac307615543ecb050ff73a1114b49cc64208c076 Mon Sep 17 00:00:00 2001
From: Tim Stirrat <tim.stirrat@gmail.com>
Date: Tue, 3 Sep 2024 10:35:04 +1000
Subject: [PATCH] Allow SysEx to pass through to mGB

Allows SysEx messages of type 0x70 to pass through to mGB
---
 Arduinoboy/Mode_MidiGb.ino | 72 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 71 insertions(+), 1 deletion(-)

diff --git a/Arduinoboy/Mode_MidiGb.ino b/Arduinoboy/Mode_MidiGb.ino
index 5df6a7b..e691445 100644
--- a/Arduinoboy/Mode_MidiGb.ino
+++ b/Arduinoboy/Mode_MidiGb.ino
@@ -36,7 +36,7 @@ void modeMidiGb()
 
       if(!checkForProgrammerSysex(incomingMidiByte) && !usbMode) serial->write(incomingMidiByte); //Echo the Byte to MIDI Output
 
-      if(incomingMidiByte & 0x80) {
+      if(incomingMidiByte & 0xF0) {
         switch (incomingMidiByte & 0xF0) {
           case 0xF0:
             midiValueMode = false;
@@ -119,6 +119,9 @@ void sendByteToGameboy(byte send_byte)
  }
 }
 
+// Are we capturing SysEx bytes?
+bool isSysexMessage = false;
+
 void modeMidiGbUsbMidiReceive()
 {
 #ifdef USE_TEENSY
@@ -195,6 +198,13 @@ void modeMidiGbUsbMidiReceive()
       do
       {
         rx = MidiUSB.read();
+        
+        maybePassThroughSysex(rx.byte1);
+        maybePassThroughSysex(rx.byte2);
+        maybePassThroughSysex(rx.byte3);
+
+        if (isSysexMessage) continue;
+
         uint8_t ch = rx.byte1 & 0x0F;
         boolean send = false;
         if(ch == memory[MEM_MGB_CH]) {
@@ -264,3 +274,63 @@ void modeMidiGbUsbMidiReceive()
       } while (rx.header != 0);
 #endif
 }
+
+#define MIDI_SYSEX_BYTE 0xF0
+#define MIDI_SYSEX_EOF 0xF7
+
+#define SYSEX_ID_NON_COMMERCIAL 0x7D
+
+// What MFG id did we find, if we find the mGB one, we'll pass through all the bits
+byte capturedSysexId = 0x00;
+
+// Passes through sysex messages to the GB if they are of the form:
+// `0xF0 0x7D ..... 0xF7`
+void maybePassThroughSysex(byte incomingMidiByte) {
+  // byte 1 - Check for SysEx status byte
+  if (!isSysexMessage && incomingMidiByte == MIDI_SYSEX_BYTE) {
+    isSysexMessage = true;
+    capturedSysexId = 0x00; // prompt check for mfg_id
+    blinkLight(0x90+2, 1);
+    return;
+  }
+
+  if (!isSysexMessage) return;
+
+  // byte 2 (mfg_id)
+  if (capturedSysexId == 0x00) {
+    capturedSysexId = incomingMidiByte;
+
+    // only if it's the right id
+    if (capturedSysexId == SYSEX_ID_NON_COMMERCIAL) {
+      // replay Sysex status byte, since we skipped it
+      sendByteToGameboy(MIDI_SYSEX_BYTE);
+      delayMicroseconds(GB_MIDI_DELAY);
+      blinkLight(0x90+2, 1);
+
+      // forward current byte (mfg id)
+      sendByteToGameboy(capturedSysexId);
+      delayMicroseconds(GB_MIDI_DELAY);
+      blinkLight(0x90+2, 1);
+    }
+    return;
+  }
+
+  // stop passthrough, wrong id
+  if (capturedSysexId != SYSEX_ID_NON_COMMERCIAL) {
+    isSysexMessage = false;
+    capturedSysexId = 0x00;
+    return;
+  }
+
+  // stop passing through, EOF
+  if (incomingMidiByte == MIDI_SYSEX_EOF) {
+    isSysexMessage = false;
+    capturedSysexId = 0x00;
+  }
+
+  // send bytes (incl EOF)
+  sendByteToGameboy(incomingMidiByte);
+  delayMicroseconds(GB_MIDI_DELAY);
+  blinkLight(0x90+2, 1);
+
+}